Apparatus and method for heating fluids



Sept. 11,1962 3,053,959

R. M. CHRISTMANN APPARATUS AND METHOD FOR HEATING FLUIDS Filed Dec. 15. 1959 A 12, Ow wi w 3,053,959 APPARATU AND METHOD FOR HEATING FLUIDS Richard M. Christmann, 616 N. Main St, Pratt, Kans. Filed Dec. 15, 1959, Ser. No. 859,645 12 Claims. (Cl. 219--I0.49)

This invention relates to an apparatus and a method for heating fluids, and, more particularly, to the heating of fluids inductively while they are flowing in a conduit.

The principal object of the invention is to provide a method and apparatus for the heating of flowing fluids which utilizes electrical energy but which is free of any connections through the wall of the conduit through which the fluids may be flowing. Although fluidcarrying pipes have been electrically heated internally for a long time, such operations have required the use of heating elements that were mechanically coupled to an electrical source and this meant the provision of connections extending through a pipe wall, or the like. This is objectionable, since it requires sealing means, involves shock and/ or spark hazard and also has been responsible for decreased efliciency of the heater. Although attempts have been made in the past to avoid this drawback, as by the utilization of the transformer principle, these attempts have been characterized by other, but equally undesirable, disadvantages which have sharply limited the use of this principle.

It is, therefore, another important object of this invention to provide a method and apparatus for heating flowing fluids which utilizes the so-called transformer" principle and which avoids the disadvantages and drawbacks experienced in previous applications of this principle. Broadly, the transformer principle comprehends the provision of a primary winding external to the liquidcarrying pipe and a secondary isolated from the primary and interposed within the pipe. In the past, attempts to utilize this principle have relied upon a dielectric effect stemming from the character of the liquid being heated. This sharply limited the liquids that could be heated, and further necessitated the employment of complex apparatus in order to generate the high frequency voltage required.

Still another object of the invention is to provide a method and apparatus for the inductive heating of flowing fluids wherein a relatively low frequency electrical current is employed. Frequencies of the order employed in power transmission, i.e., 60 cycles per second, are uniformly available, and the use of such electrical energy for inductive heating according to the so-called transformer principle is an object hereof.

Yet another object is to provide a method and apparatus for inductive heating of liquids flowing in a pipe, or the like, in which a novel transformer secondary is installed in the pipe to provide a desirably high efliciency in the heating operation.

Other objects and advantages of this invention may be .seen in the details of construction and operation as set 22 which are effective to pot the coil on the tube.

Patented Sept. 11, 1952 ice be employed for the conduction of a liquid such as water from an entry point 11 to a discharge point 12. For the purpose of inducing liquid flow in the piping system 10, a pump 13 is provided. Also interposed in the piping system 10 is a heater generally designated by the numeral 14, which is electrically energized by a generator 15. Inasmuch as a principal object of this invention is to pro vide a novel method and apparatus for the heating of flowing fluids, it is believed unnecessary to go into further detail relative to the piping system it} or ramifications thereof. Many modifications of the system depicted will occur to those skilled in the art as a result of a consideration of the instant teaching.

The system 10 may include conventional iron pipe lengths such as are designated by the numeral 16. Also, the system 10 may include iron elbows 17 and a conventional union 18.

The portion of the system lltl including the heater 14 can be seen in enlarged scale in FIG. 2, Where the iron or other pipe 16 is seen connected as by threads 19 to a pipe length 20. The pipe length 20 is seen to be shaded for a nonconducting material of construction such as Fiberglas.

Disposed about the pipe 20 is a coil 21, a portion of one winding 21:: being seen in the cross-sectional view depicted in FIG. 3. The coil 21 is insulated from the atmosphere by means of an insulating layer 22. The layer 22 also assures insulation of each winding or convolution 21a from an adjacent Winding or convolution. A variety of suitable materials can be used for the layer A commercially available material for this purpose is epoxy resin and is effective to seal the coil 21 hermetically as well as electrically and thermally insulate the same. Also, the layer 22 mechanically ruggedizes the pipe-coil combination. In this manner, the primary of the transformer provided by the coil 21 is integrated with the fluidconducting pipe 20. The coil 21 is connected by means of leads 23 to a source of alternating current which, for the sake of convenience, is depicted as a generator 15. The generator 15 may be either adjacent to or remote from the heater 14the latter being the case where commercial electric power is employed. The heater 14 has been designed to operate effectively with ordinary power line frequency, i.e., 60 cycles per second. Other low frequency currents can be also employed to advantage, such as 25 or 400 cycles per second. Through the use of this frequency energy, it is possible to develop up to 20 kilowatts of power in a pipe heater while still retaining modest size and insuring that the over-all installation is desirably rugged.

The secondary is provided in the form illustrated as ,an inner pipe 24 which is spaced or supported interiorly .(when the primary coil 21 is energized) through a circulating current in the surface shell of the secondary element 24 as if the same were acting as a one turn secondary. Here, it is to be appreciated that the secondary element 24 is in effect a core which provides its own secondary, and, thus, if desired, a special secondary Wind- .ing may be omitted.

This core element 24 may be treated in a variety of manners to insure chemical inertness, e.g., gold plating may be used for water-heating cores; or for oil, copper could be used. A variety of inert materials may be employed for the spacers 25, such as Teflon. From this, it will be seen that the heating element is effectively insulated both from the pipes 16 of the piping system and from the primary-providing coil 21.

Through the use of a single element providing both the secondary and the core, it is now possible to provide a device employing the transformer principle which is capable of dissipating heat at a reasonable power level within the pipe carrying the liquid to be heated and while yet retaining a very desirable compactness and ruggedness so as to make commercial utilization feasible. It is now possible to provide an in-line pipe heater through the assembly of three single partsthe pipe, the winding, and the core. Alternatively, this could be done through the employment of two major partsthe potted pipewinding and the treated core.

For optimum operation, the core should have a size, i.e., area and length, to operate just under saturation for the voltage employed. This insures that maximum economy of weight and over-all size may be maintained. This also precludes operation in an area when there is a nonlinear current voltage relationship which may prove injurious to the equipment. Also, the core is desirably constructed to be at least as much longer than the winding on each end of the winding as is the inside diameter of the winding. This can be appreciated from a con sideration of FIGURE 2 wherein the overlap of the core relative to the coil 21 is designated by the numeral 26- this being indicated at only the left hand end of the coreproviding element 24 but which is seen to exist also at the right hand end thereof. In this fashion, I am able to minimize end flux loss effects and to maximize the power factor. Lengths greater than that shown provide little, if any, additional improvement in power factor. Heaters have been constructed according to these conditions operating with power factors of 0.9 or better and with conversion efficiencies of virtually 100%.

If desired, the heating capacity of the heater 14 may be enhanced by interposing a one turn cylindrical shell of a non-magnetic conductor such as a brass tube. This is indicated in dotted line in FIGURE 3 by the numeral 27. Such a modification, however, may tend to complicate the structure and might only be advisable where an absolute maximum in space economy is required. Usually, however, such supplemental structure is not needed. This may be appreciated from the fact that a heater effective to deliver 37,500 Btu per hour need be only 30 inches long with a 24 inch long potted primary having an OD. of about 3 inches.

Effective instant heating may be obtained by the addition of the interposed shell 27 or, to a lesser degree, by the plating or coating of a heavy film of low resistivity material on the core 24. The normal time response of the heater (23 seconds) may be improved by a factor of 3 or 4 in this manner.

The heater of the invention is exceptionally advantageous since it does not require costly frequency conversion, special winding procedures or core treatments, special conduit shapes, or special separate components. It provides the heater with large heat exchange area for minimum hot spot effect. It is susceptible of being made as chemically inert as the user desires and may be made around other types of non-magnetic, non-conductor pipe and treated to resist even such highly corrosive materials as hydrogen fluoride, aquaregia, etc. It is of advantageous use in full flow heating application, imposing minimum pressure drop, or to demand heating, such as in hotels, homes, etc. Here, it is to be appreciated that maximum efiiciency in transfer of heat to the fluid flowing past the secondary is achieved without the need for introducing substantial friction. Somewhat less than .5 psi. head is sufiicient to attain approximately 30 g.p.m. flow through a 10 kw. heater with a flow area equivalent to a pipe of about inch I.D. In most fluid flow opera tions, it is undesirable to introduce frictional resistance but the same is often necessary to reduce film coefficient so as to achieve substantial heat transfer. With the instant invention, streamline-as contrasted to turbulent flow-can be employed without effecting the achievement of maximum efficiency of heat transfer.

While in the foregoing specification I have set forth a detailed description of an embodiment of the invention for the purpose of completely describing the same, it will be apparent to those skilled in the art that many variations of the details herein given may be made without departing from the spirit and scope of the invention.

I claim:

1. In a fluid heater, a conduit constructed of electrical insulating material, an electrical winding about said conduit, a source of low frequency voltage coupled to said winding, a magnetic element within said conduit, and a nonmagnetic element about said magnetic element and within said conduit, the inner walls of said conduit being spaced from the outer walls of said nonmagnetic element whereby fluid is adapted to flow between said inner and outer Walls, said electrical winding being effective to inductively heat fluid flowing past said elements.

2. The structure of claim 1 in which said nonmagnetic element is a brass cylinder.

3. In a fluid heater, a conduit constructed of electrical insulating material, an electrical winding about said conduit, a source of low frequency voltage coupled to said winding, and an element within said conduit in the path of fluid flowing therein to direct fluid flow about said element, said element being constructed of magnetic material, said conduit being a circular pipe, said element overlapping said winding at each end of the winding by at least about the inside diameter of said winding.

4. In a device for heating fluids flowing in a conduit, a length of conduit constructed of nonmagnetic electrical insulating material, a length of electrical conductor Wound about said length of conduit with each winding loop being insulated from the remaining loops, a source of alternating current coupled to said electrical conductor whereby the said electrical conductor is effective to serve as a transformer primary, and a transformer secondary constructed of magnetic material in said length of conduit and heatable primarily by eddy currents induced therein by said primary, said secondary being interposed in the path of fluid flowing in said conduit and having its outer walls spaced from the inner walls of said conduit, whereby said fluid necessarily flows around said secondary.

5. In a device for heating fluids flowing in a conduit, a length of conduit constructed of nonmagnetic electrical insulating material, a length of electrical conductor wound about said length of conduit with each winding loop being insulated from the remaining loops, a source of alternating current of power line frequency coupled to said electrical conductor whereby the said electrical conductor is effective to serve as a transformer primary, and a transformer secondary constructed of magnetic material in said length of conduit, said secondary being interposed in the path of fluid flowing in said conduit and having its outer walls spaced from the inner walls of said conductor, whereby said fluid necessarily flows around said secondary.

6. In a device for heating fluids flowing in a conduit, a length of conduit constructed of nonmagnetic electrical insulating material, a length of electrical conductor wound about said length of conduit with each winding loop being insulated from the remaining loops, a source of alternating current coupled to said electrical conductor whereby the said electrical conductor is effective to serve as a transformer primary, and a solid bar transformer secondary constructed of magnetic material in said length of conduit, said secondary being interposed in the path of fluid flowing in said conduit and having its outer Walls spaced from the inner Walls of said conduit, whereby said fluid necessarily flows around said secondary.

7. In a device for heating fluids flowing in a conduit, a length of conduit constructed of nonmagnetic electrical insulating material, a length of electrical conductor Wound about said length of conduit with each winding loop being insulated from the remaining loops, a source of alternating current coupled to said electrical conductor whereby the said electrical conductor is eiiective to serve as a transformer primary, and a magnetic element serving as a core of said transformer and located centrally of said conduit, said magnetic element being equipped with a nonmagnetic outer surface serving as the secondary of said transformer, said secondary being interposed in the path of fluid flowing in said conduit and having its outer Walls spaced from the inner walls of said conduit, whereby said fluid necessarily flows around said secondary.

8. In a device for heating fluids flowing in a conduit, a length of circular conduit constructed of nonmagnetic electrical insulating material, a length of electrical conductor wound about said length of conduit with each Winding loop being insulated from the remaining loops, a source of alternating current of power line frequency coupled to said electrical conductor whereby the said electrical conductor is effective to serve as a transformer primary, and a solid transformer secondary constructed of magnetic material in said length of conduit, said secondary being interposed in the path of fluid flowing in said conduit and having its outer walls spaced from the inner walls of said conduit, whereby said fluid necessarily flows around said secondary, said element overlapping the Wound length of electrical conductor at each end of the Winding by at least about the inside diameter of said winding.

9. In a fluid heater, a conduit constructed of electrical insulating material, an electrical winding about said conduit, a source of low frequency voltage coupled to said Winding, and an element within said conduit in the path of fluid flowing therein to direct fluid flow about said element, said element being constructed of magnetic material and adapted to be inductively heated by current flowing in said Winding, said element being rigidly mounted in said conduit and defining with said conduit a fluid flow channel wherein the fluid flowing in said channel is heated substantially entirely by electrical currents induced in said element.

10. The structure of claim 9 in which said element is proportioned in area and length for operation just under saturation for the voltage employed.

11. The structure of claim 9 in which said element is elongated relative to said winding in the direction of fluid flow and is positioned in said conduit to overlap said winding at both ends of said Winding.

12. The structure of: claim 11 in which the ratio of winding length to winding diameter is about eight.

References tCited in the file of this patent UNITED STATES PATENTS 1,260,564 Magnusson et al Mar. 26, 1918 2,181,274 Jackson et al. Nov. 28, 1939 2,218,999 White Oct. 22, 1940 2,868,938 Barfield et al Jan. 13, 1959 2,875,311 Harkenrider Feb. 24, 1959 2,904,664 Rothacker Sept. 15, 1959 

